1. Field of the Invention
This invention relates to hydraulic pumps for providing hydraulic fluid under pressure to a hydraulic torque wrench, and in particular to such a pump which is air powered.
2. Discussion of the Prior Art
Air powered hydraulic torque wrench pumps for providing hydraulic fluid under pressure to operate a hydraulic torque wrench are known. Such a pump is connected to a source of compressed air, which is common in industry, and the compressed air drives an air motor of the pump which is mechanically coupled to drive a hydraulic pump. Operation of the hydraulic pump provides hydraulic fluid under pressure from a hydraulic fluid reservoir which is typically incorporated into the pump assembly. The air motor is typically a rotary air motor which is mechanically coupled to a rotary hydraulic pump, although linear air motors and hydraulic pumps are also possible.
In such pump assemblies, once the air motor is turned on, the pump typically continues to operate until the supply of air to the air motor is turned off by the operator. Since continuous operation of the hydraulic pump generates considerable heat in the hydraulic fluid which is being pumped, a heat exchanger has been provided as part of the pump assembly so as to provide cooling for the hydraulic fluid when the pump is operated for a long period of time. In these units, continuous operation of the pump was common, even though tightening of the fasteners using the hydraulic wrench was only intermittent. As a result, not only was the provision of the heat exchanger made necessary, but energy operating the pump during the periods that a fastener was not being tightened was wasted.